We currently do not have a way to do this (yet). We’re working on a solution for that in the future, though. You can inspect the Manifest files on the download servers if you really want to know, but that’s probably not what you want.
Just open it in a text editor after downloading, and you get the idea of how it works. There’s more info in the swupd-client project describing the format. mixer-tools also has more info.